Alpha-Adrenergic receptors and prostaglandin receptors were studied in human blood cell preparations. The ability of adrenergic agonists to inhibit adenylate cyclase was used as a measure of the alpha2-receptors' biological function. Binding of tritiated alpha-adrenergic receptor antagonists to membrane receptors on platelets was measured. These measures were correlated and are used to assess Alpha2 adrenergic physiological function in normal individuals, patients with various psychiatric disorders, and diseases of neurotransmission and patients receiving different psychopharmacologic agents.